This application claims the benefit of Korean Patent Application No. 2000-76879, filed on Dec. 15, 2000 in Korea, which is hereby incorporated by reference as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a liquid crystal panel for a liquid crystal display device implementing In-Plane Switching (IPS) wherein electric field applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of the Related Art
A typical liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientation order in alignment resulting from their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by supplying an electric field to the liquid crystal molecules. In other words, as the alignment direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Because incident light is refracted to the orientation of the liquid crystal molecules due to the optical anisotropy of the aligned liquid crystal molecules, image data is displayed.
By now, active matrix LCDs, in which the thin film transistors and the pixel electrodes are arranged in the form of a matrix, are widely used because of their high resolution and superiority in displaying moving images.
FIG. 1 is an exploded perspective view illustrating a typical liquid crystal display device. As shown in the figure, the typical liquid crystal display device includes an upper substrate 5 and a lower substrate 22 and a liquid crystal layer 14 interposed between the upper and lower substrate. A color filter 7 including black matrices 6 and sub-filters 8 are formed on the upper substrate 5, and a transparent common electrode 18 is formed on the color filter 7. On the other hand, a pixel region xe2x80x9cPxe2x80x9d, a pixel electrode 17 in the pixel region xe2x80x9cPxe2x80x9d and an array line including switching element, i.e., thin film transistor, are formed on the lower substrate 22. The lower substrate 22 is referred to as an array substrate 22 and a plurality of thin film transistors xe2x80x9cTxe2x80x9d, i.e., switching element, is formed at every crossing of horizontal gate lines 13 and vertical data lines 15 in a form of an array matrix. The pixel region xe2x80x9cPxe2x80x9d is defined by a gate line 13 and a data line 15 crossing each other. A transparent conductive material such as indium tin oxide (ITO) is used for the pixel electrode 17 formed in the pixel region xe2x80x9cPxe2x80x9d. The liquid crystal layer 14 comes to be aligned according to a signal applied thereto by the thin film transistor xe2x80x9cTxe2x80x9d. An image may be displayed by controlling an amount of light transmitting the liquid crystal layer 14 according to the alignment of the liquid crystal layer.
The above-mentioned liquid crystal display device, in which the liquid crystal is aligned by an electric field applied vertically, has advantages of high transmittance and high aperture ratio. Furthermore, since the common electrode on the upper substrate serves as an electrical ground, the liquid crystal is protected from a static electricity. However, the above-mentioned liquid crystal display device applying the electric field vertically to the liquid crystal has a disadvantage of a narrow viewing angle. To overcome the narrow viewing angle, an in-plane switching (IPS) LCD panel was developed. The IPS LCD panel implements an electric field that is parallel to the substrates, which is different from the Twisted Nematic (TN) or Super Twisted Nematic (STN) LCD panel. A detailed explanation about operation modes of a typical IPS LCD panel will be provided with reference to FIGS. 2, 3A, 3B, and 4.
As shown in FIG. 2, the upper and lower substrates 5 and 22 are spaced apart from each other, and a liquid crystal is interposed therebetween. The upper and lower substrates 5 and 22 are called a color filter substrate and an array substrate, respectively. Pixel and common electrodes 17 and 18 are disposed on the lower substrate 22. The pixel and common electrodes 17 and 18 are parallel with each other and spaced apart from each other. The liquid crystal 14 is aligned by a lateral electric field between the pixel and common electrodes 17 and 18.
FIGS. 3A to 3B are views illustrating operations of the liquid crystal for IPS mode at on and off state of a voltage applied. FIG. 3A conceptually illustrates xe2x80x9coff statexe2x80x9d operation modes for a typical IPS LCD device. In the off state, the long axes of the liquid crystal molecules maintain a definite angle with respect to a line that is perpendicular to the pixel and common electrodes 17 and 18. The pixel and common electrode 17 and 18 are parallel with each other. Herein, the angle difference is 45 degrees, for example.
FIG. 3B conceptually illustrates xe2x80x9con statexe2x80x9d operation modes for the typical IPS LCD device. In the on state, an in-plane electric field, which is parallel with the surface of the lower substrate 22, is generated between the pixel and common electrodes 17 and 18. The reason is that the pixel electrode 17 and common electrode 18 are formed together on the lower substrate 22. The liquid crystal molecules are twisted such that the long axes thereof coincide with the electric field direction. Thereby, the liquid crystal molecules are aligned such that the long axes thereof are perpendicular to the pixel and common electrodes 17 and 18.
The IPS LCD device uses the lateral electric field 35 because the pixel and common electrodes are formed on the same substrate. The IPS LCD device has a wide viewing angle and low color dispersion. Specifically, the viewing angle of the IPS LCD device is about 70 degrees in direction of up, down, right, and left. In addition, the fabricating processes of this IPS LCD device are simpler than other various LCD devices. However, because the pixel and common electrodes 17 and 18 are disposed on the same plane of the lower substrate, the transmittance and aperture ratio are low. In addition, the IPS LCD device has disadvantages of a relatively slow response time and a relatively small alignment margin of a cell gap. Because of the small alignment margin of a cell gap, the IPS LCD device needs a uniform cell gap. The IPS LCD device has the above-mentioned advantages and disadvantages. Users may or may not select an IPS LCD device depending on the intended use.
Now, with reference to FIGS. 4, and 5A to 5D, a fabricating process for a conventional IPS LCD device is provided. FIG. 4 is a plan view illustrating a unit pixel region xe2x80x9cPxe2x80x9d of a conventional IPS LCD device. As shown, a gate line 50 and a common line 54 are arranged parallel to each other, and a data line 60 is arranged perpendicular to the gate and common lines 50 and 54. Near a cross point of the gate and data lines 50 and 60, a gate electrode 52 and a source electrode 62 are disposed. The gate and source electrodes 52 and 62 integrally communicate with the gate line 50 and the data line 60, respectively. The source electrode 62 overlaps a portion of the gate electrode 52. In addition, a drain electrode 64 is disposed opposite to the source electrode 62 with an interval between the source and drain electrodes.
A plurality of common electrodes 54a are disposed perpendicular to the common line 54 and connected to the common line 54. The plurality of common electrodes 54a are spaced apart from each other with an equal interval between. A first connecting line 66 integrally communicates with the drain electrode 64. A plurality of pixel electrodes 66a are disposed perpendicular to the first connecting line 66. First ends of the pixel electrodes 66a are connected with the first connecting line 66, and the second ends of the pixel electrodes 66a are connected with a second connecting line 68 that is disposed over the common line 54. The plurality of common electrodes 54a and the pixel electrodes 66a are spaced apart from each other and arranged in an alternating pattern. Therefore, each common electrode 54a is parallel to an adjacent pixel electrode 66a. 
FIGS. 5A to 5D are cross-sectional views taken along xe2x80x9cVxe2x80x94Vxe2x80x9d of FIG. 4 illustrating a sequence of fabricating processes for an array substrate 22 of the above-mentioned IPS LCD device.
In FIG. 5A, a first metal layer is deposited on the array substrate 22 and patterned to form the gate electrode 52 and the plurality of common electrodes 54a. The first metal layer may be selected from a group consisting of chromium (Cr), aluminum (Al), aluminum alloy (Al alloy), for example.
In FIG. 5B, a gate insulating layer 70 is formed on the array substrate 22 to cover the gate and common electrodes 52 and 54a. An active layer 72 is formed on the gate insulating layer 70 over the gate electrode 52. Silicon nitride (SiNx), for example, may be used for the gate insulating layer 70, while the active layer 72 includes an amorphous silicon layer (not shown) and a doped amorphous silicon layer (not shown).
In FIG. 5C, a second metal layer is deposited and patterned to form the source and drain electrodes 62 and 64 on the active layer 72 and the pixel electrodes 66a on the gate insulating layer 70. The pixel electrodes 66a are spaced apart from the adjacent common electrode 54a by a distance xe2x80x9cLxe2x80x9d.
In FIG. 5D, a passivation layer 74 is formed to cover the source, drain, and pixel electrodes 62, 64, and 66a. The passivation layer 74 serves to protect the source, drain, and pixel electrodes 62, 64, and 66a from exterior humidity or contaminants.
As described above, the common and pixel electrodes 54a and 66a of the IPS LCD device are arranged in the same plane such that an in-plane electric field is applied parallel with the substrate 22. Though the IPS LCD device has an advantage of a wide viewing angle, the aperture ratio and luminance of the IPS LCD panel are much lower than that of the twisted nematic (TN) or super twisted nematic (STN) LCD device.
Accordingly, the present invention is directed to an in-plane switching (IPS) mode liquid crystal display device and a method for fabricating the same that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide an in-plane switching liquid crystal display device that improves an aperture ratio and brightness as well as a viewing angle.
Another advantage of the present invention is to provide a fabricating method for an in-plane switching liquid crystal display device that improves the aperture ratio and the brightness.
Another advantage of the present invention is to provide an in-plane switching liquid crystal display device that further improves the aperture ratio and the brightness.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an in-plane switching liquid crystal display device comprises first and second substrates, a gate line and a data line defining a pixel region on the first substrate, a common line on the first substrate, a thin film transistor at a crossing portion between the gate line and the data line, a first pixel electrode and a plurality of second pixel electrodes on the first substrate, a first common electrode and a plurality of second common electrodes on the first substrate, a black matrix layer on the second substrate, the black matrix layer having a substantially rectangular shape and being formed between the first pixel electrode and one end of the second common electrode and a liquid crystal layer between the first substrate and the second substrate. The common line is partially overlapped with the data line. The thin film transistor includes gate, source, and drain electrodes. The pixel and common electrodes include a transparent conductive material. The transparent conductive material is one of indium tin oxide (ITO) and indium zinc oxide (IZO). The common line and the data line have a zigzag shape. The pixel and common electrodes have a substantially zigzag shape. The black matrix layer is formed between one end of the second pixel electrode and the first common electrode. The in-plane switching liquid crystal display device further includes a storage capacitor on the gate line. The in-plane switching liquid crystal display device further includes a passivation layer on the thin film transistor. The common and pixel electrodes are formed on the passivation layer.
In another aspect, a method for fabricating an in-plane switching liquid crystal display device includes the steps of forming a gate line and a data line defining a pixel region on a first substrate, forming a common line on the first substrate, forming a thin film transistor at a crossing portion between the gate line and the data line, forming a first pixel electrode and a plurality of second pixel electrodes on the first substrate, forming a first common electrode and a plurality of second common electrodes on the first substrate, forming a black matrix layer on the second substrate, the black matrix layer having a substantially rectangular shape and being formed between the first pixel electrode and one end of the second common electrode and forming a liquid crystal layer between the first and second substrates. The pixel and common electrodes include a transparent conductive material. The transparent conductive material is one of indium tin oxide (ITO) and indium zinc oxide (IZO). The common line and the data line have a substantially zigzag shape. The pixel and common electrodes have a substantially zigzag shape. The black matrix layer is formed between one end of the second pixel electrode and the first common electrode. The method for fabricating an in-plane switching liquid crystal display device further includes the step of forming a storage capacitor on the gate line. The method for fabricating an in-plane switching liquid crystal display device further includes the step of forming a passivation layer on the thin film transistor. The common and pixel electrodes are formed on the passivation layer.
In another aspect, an in-plane switching liquid crystal display device includes first and second substrates, a gate line and a data line defining a pixel region on the first substrate, a common line on the first substrate, a thin film transistor at a crossing portion between the gate line and the data line, a first pixel electrode and a plurality of second pixel electrodes on the first substrate, a first common electrode and a plurality of second common electrodes on the first substrate, a black matrix layer on the first substrate, the black matrix layer being formed between the first pixel electrode and one end of the second common electrode and a liquid crystal layer between the first substrate and the second substrate. The common line is partially overlapped with the data line. The thin film transistor includes gate, source, and drain electrodes. The pixel and common electrodes include a transparent conductive material. The transparent conductive material is one of indium tin oxide (ITO) and indium zinc oxide (IZO). The common line and the data line have a substantially zigzag shape. The pixel and common electrodes have a substantially zigzag shape. The black matrix layer is formed between one end of the second pixel electrode and the first common electrode. The black matrix layer is formed on the same plane of the gate line. The black matrix layer is formed on the same plane of the data line. The in-plane switching liquid crystal display device further comprises a passivation layer on the thin film transistor. The common and pixel electrodes are formed on the passivation layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.